The present invention relates to an improved process for making granular detergent compositions which have superior solubility, especially in cold temperature laundering solutions (i.e., less than about 30xc2x0 C.), excellent flow properties (even after storage), and aesthetics/appearance. More particularly, the present process results in detergent compositions containing optimal levels of particles having optimally selected particle size and particle size distribution for achieving the desired improvements.
Recently, there has been considerable interest within the detergent industry for laundry detergents which have the convenience, aesthetics and solubility of liquid laundry detergent products, but retain the cleaning performance and cost of granular detergent products. The problems, however, associated with past granular detergent compositions with regard to aesthetics, solubility, flowability after standard storage conditions and user convenience are formidable. Such problems have been exacerbated by the advent of xe2x80x9ccompactxe2x80x9d or low dosage granular detergent products which typically do not dissolve in washing solutions as well as their liquid laundry detergent counterparts. These low dosage detergents are currently in high demand as they conserve resources and can be sold in small packages which are more convenient for consumers prior to use, but less convenient upon dispensing into the washing machine as compared to liquid laundry detergent which can be simply poured directly from the bottle as opposed to xe2x80x9cscoopedxe2x80x9d from the box and then dispensed into the washing solution.
As mentioned, such low dosage or xe2x80x9ccompactxe2x80x9d detergent products unfortunately experience dissolution problems, especially in cold temperature laundering solutions (i.e., less than about 30xc2x0 C.). More specifically, poor dissolution results in the formation of xe2x80x9cclumpsxe2x80x9d which appear as solid white masses remaining in the washing machine or on the laundered clothes after conventional washing cycles. These xe2x80x9cclumpsxe2x80x9d are especially prevalent under cold temperature washing conditions and/or when the order of addition to the washing machine is laundry detergent first, clothes second and water last (commonly known as the xe2x80x9cReverse Order Of Additionxe2x80x9d or xe2x80x9cROOAxe2x80x9d). Such undesirable xe2x80x9cclumpsxe2x80x9d are also formed if the consumer loads the washing machine in the order of clothes, detergent and then water. Similarly, this clumping phenomenon can contribute to the incomplete dispensing of detergent in washing machines equipped with dispenser drawers or in other dispensing devices, such as a granulette. In this case, the undesired result is undissolved detergent residue in the dispensing device.
It has been found that the cause of the aforementioned dissolution problem is associated at least in part with the xe2x80x9cbridgingxe2x80x9d of a xe2x80x9cgel-likexe2x80x9d substance between surfactant-containing particles to form undesirable xe2x80x9cclumps.xe2x80x9d The gel-like substance responsible for the undesirable xe2x80x9cbridgingxe2x80x9d of particles into xe2x80x9cclumpsxe2x80x9d originates from the partial dissolution of surfactant in the aqueous laundering solutions, wherein such partial dissolution causes the formation of a highly viscous surfactant phase or paste which binds or otherwise xe2x80x9cbridgesxe2x80x9d other surfactant-containing particles together into xe2x80x9cclumps.xe2x80x9d This undesirable dissolution phenomena is commonly referred to as xe2x80x9clump-gelxe2x80x9d formation. In addition to the viscous surfactant xe2x80x9cbridgingxe2x80x9d effect, inorganic salts have a tendency to hydrate which can also cause xe2x80x9cbridgingxe2x80x9d of particles which linked together via hydration. In particular, inorganic salts hydrate with one another to form a cage structure which exhibits poor dissolution and ultimately ends up as a xe2x80x9cclumpxe2x80x9d after the washing cycle. It would therefore be desirable to have a detergent composition which does not experience the dissolution problems identified above so as to result in improved cleaning performance.
The prior art is replete with disclosures addressing the dissolution problems associated with granular detergent compositions. For example, the prior art suggests limiting the use and manner of inorganic salts which can cause clumps via the xe2x80x9cbridgingxe2x80x9d of hydrated salts during the laundering cycle. Specific ratios of selected inorganic salts are contemplated so as to minimize dissolution problems. Such a solution, however, constricts the formulation and process flexibility which are necessary for current commercialization of large-scale detergent products. Various other mechanisms have been suggested by the prior art, all of which involve formulation alteration, and thereby reduce formulation flexibility. As a consequence, it would therefore be desirable to have a process for making detergent compositions having improved dissolution without significantly inhibiting formulation flexibility.
Accordingly, despite the disclosures in the prior art discussed previously, it would be desirable to have a process for making a granular detergent composition which exhibits improved solubility, is more aesthetically pleasing to consumers, has improved flowability and exhibits improved cleaning performance. Also, it would be desirable to have such a process having substantial process flexibility yet still resulting in a detergent composition which exhibits improved dissolution without significantly inhibiting formulation flexibility.
The invention meets the needs above by providing a process for making a detergent composition which has improved solubility or dissolution in laundering solutions, especially in solutions kept at cold temperatures (i.e., less than about 30xc2x0 C.), is aesthetically pleasing to consumers and has improved flowability. The process for making the granular detergent compositions has substantial flexibility yet results in an optimally selected level of particles having a judiciously selected geometric mean particle diameter with a selected geometric standard deviation.
In accordance with one aspect of the invention, there is provided a process for making a granular detergent composition comprising the steps of:
a) adding to a mixer a first feed stream comprising a component selected from the group consisting of a first powder, a first liquid, and mixtures thereof, to form a second feed stream;
b) adding the second feed stream to a fluid bed dryer to form the granular detergent composition;
c) optionally, adding to the fluid bed dryer a third feed stream comprising a component selected from the group consisting of a second powder, a second liquid, and mixtures thereof; and
wherein the resulting granular detergent composition comprises at least about 50%, preferably 75%, and most preferably 90%, by weight of particles having a geometric mean particle diameter of from about 500 microns to about 1500 microns, preferably the geometric mean particle diameter of the particles are from about 600 microns to about 1200 microns, and most preferably, from about 700 microns to about 1000 microns, with a geometric standard deviation of from about 1 to about 2, preferably from about 1.0 to 1.7, and more preferably from about 1.0 to about 1.4, wherein at least a portion of the particles contain a detersive surfactant or a detergent builder. Preferably the first powder and the second powder each comprise a material selected from the group consisting of surfactants, inorganic salts, bleaches, bleach activators, builders, enzymes, encapsulated perfumes, and mixtures thereof, and the first liquid and the second liquid each comprise a material selected from the group consisting of water, surfactants, inorganic salts, dyes, polymers, builders, binders, perfumes, and mixtures thereof. Most preferably the added liquids comprise detergent surfactants in an aqueous paste form.
The invention also provides a method of laundering soiled fabrics comprising the step of contacting the soiled fabrics with an aqueous solution containing an effective amount of a detergent composition made according to the invention described herein.
Accordingly, it is an advantage of the invention to provide a process for making granular detergent compositions which exhibit improved solubility, are more aesthetically pleasing to consumers, have improved flowability and exhibit improved cleaning performance. It is also an advantage to have such a detergent composition which exhibits such improved dissolution without significantly inhibiting formulation flexibility.